150 PHILOSOPHICAL TRANSACTIONS. [ANNO 1781. 



which were established by these experiments. Some have attributed the cold 

 solely to evaporation, and have conceived that the same degree of refrigeration 

 would have been produced by an equal mass of dead matter, containing an equal 

 quantity of moisture. Others have affirmed, that the cold did not arise solely 

 from this cause; but have maintained, that it depended partly on the energy of 

 the vital principle, being greater than what would have been produced by an 

 equal mass of inanimate matter. The ingenious Dr. Munro, of Edinburgh, 

 ascribes the cold in the above-mentioned experiments to the circulation of the 

 blood, in consequence of which the warmer fluids are continually propelled from 

 the surface towards the centre, where they are mixed with blood at a lower tem- 

 perature, and hence the animal is slowly heated, in the same manner as the 

 water in a deep lake, during the winter, is slowly cooled, and not without a long 

 continuance of frost congealed, no part of it becoming solid till the whole is 

 brought down to the freezing point. 



The following experiments were made with a view to determine with greater 

 certainty the causes of the refrigeration in the above instances. To discover 

 whether the cold produced by a living animal, placed in air hotter than its 

 body, be not greater than what would be produced by an equal mass of in- 

 animate matter, Dr. C. took a living and a dead frog, equally moist, and of 

 nearly the same bulk, the former of which was 

 at 67°, the latter at 68°, and laid them on In \ 

 flannel in air which had been raised to 106°. 

 In the course of 25 minutes the order of heat- 

 ing was as annexed.* 



The thermometer being introduced into the stomach, the internal heat of the 

 animals was found to be the same with that at the surface. Hence it appears, 

 that the living frog acquired heat more slowly than the dead one. Its vital 

 powers must therefore have been active in the generation of cold. 



To determine whether the cold produced in 

 this instance depended solely on the evapora- 

 tion from the surface, increased by the energy 

 of the vital principle, a living and dead frog 

 were taken at 75°, and were immersed in water 

 at Q3°, the living frog being placed in such a 

 situation as not to interrupt respiration. -j~ 



These experiments prove, that living frogs have the faculty of resisting heat, 



* In the two following experiments the thermometers were placed in contact with the skin of the 

 animals under the axillae. — Orig. 



-j- In the above experiment the water, by the cold frogs and by the agitation which it suffered during 

 their immersion, was reduced nearly to yi"j. — Orig. 



